Under a condition where a battery is charged while limiting the power supplied from external AC power supply PSUP to allowable charge power PLIM, and when drive of a PTC heater is requested and the PTC heater is driven in pulse drive by PWM control, the battery changes so that drive power of the PTC heater pulsates at a constant cycle by the PWM control. In such a case, for a part where drive power of the PTC heater is maximized, a battery charge system maintains a state in which charge power to the battery does not exceed the allowable charging power PLIM by discharging the battery
In the conventional system described above, when driving with the PTC heater, by putting the battery into a discharge state so as not to allow charge power of the battery to exceed the allowable charging power PLIM by pulsation occurred by switching operation of the PWM control, charge voltage of the battery is controlled so as not to exceed the upper limit charge voltage. Also, by assuming that a size of pulsation due to switching operation of the PWM control is constant, charge power of the battery is controlled not to exceed the allowable charge power PLIM.
Whereas, in a charge system for charging a battery while rectifying AC power by a full-wave rectifying method or half-wave rectifying method, charge power also pulsates along with rectification. In such charge system, when the battery is put into a discharge state so as not to allow charge voltage of the battery to exceed the upper limit charge power as in the above conventional system, the power actually charged to the battery (charge efficiency) decreases relative to the charge power and an amount of power that can be charged to a battery per unit hour decreases. More, while assuming that the size of pulsation is constant as in the conventional system, and when the upper limit charge voltage is limited low for the constant amount of pulsation in the above charge system, voltage chargeable to the battery becomes low relative to the actual pulsation magnitude. Subsequently, there are problems that the amount of power chargeable to the battery decreases and accordingly, and the amount of power charged to the battery decreases at completion of the charge.